1. Field of the Invention
The present invention relates generally to a mobile communication system employing Code Division Multiple Access (CDMA). In particular, the present invention relates to a method and apparatus in which a terminal (or user equipment (UE)) reports measurement results to the system.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system, which is an asynchronous 3rd generation (3G) mobile communication system employing Wideband Code Division Multiple Access (WCDMA) based on European Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS), provides consistent service that is capable of allowing telephone or computer users to transmit packet switched text, digitized voice, video, and multimedia data, at rates of about 2 Mbps all over the world. UMTS uses a virtual access technology, the so-called packet switched access based on a packet protocol such as Internet Protocol (IP), and can always access any other terminals in the network.
In the 3rd Generation Project Partnership (3GPP), the standard for the asynchronous 3G mobile communication system, a Random Access Channel (RACH) which is an uplink common channel, is used for network access and control and transmission of short-length data. Such logical channels, for example a Dedicated Control Channel (DCCH), a Common Control Channel (CCCH), and a Dedicated Traffic Channel (DTCH), can be mapped to the RACH which is a transport channel.
The RACH can be used for measurement reporting. That is, a UE includes measurement results indicating its measured radio strengths of other cells and other frequencies in a Radio Resource Control (RRC) message for signaling, transmitted to a Radio Network Controller (RNC) over the RACH. The measurement results are used by the system to determine whether a communication environment of a UE is good, and whether the UE is located in a handover region. Measurement control system information needed for performing inter-frequency and intra-frequency measurements is included in system information blocks (SIB) received from the RNC. The UE, in an idle mode or a connected mode, receives a SIB transmitted over a broadcast channel and acquires the measurement control system information therefrom.
Table 1 and Table 2 below show, by way of example, a format of a RACH message for reporting inter-frequency measurement system information and inter-frequency measurement results, included in SIB11/12 to be used for reporting the inter-frequency measurement results. SIB11/12 includes measurement-related control information used in the current cell, wherein SIB11 is for an idle mode UE and SIB12 is for a connected mode UE. If there is no SIB12, the connected mode UE also refers to SIB11.
Table 1 consists of Table 1a to Table 1c. Table 1a shows a format of ‘Inter-frequency measurement system information’ included in SIB11/12. In Table 1a, an ‘Inter-frequency reporting quantity for RACH reporting’ information element (IE) and a ‘maximum number of inter-frequency reported cells on RACH’ IE are information for including inter-frequency measurement result values in the RACH message.
TABLE 1aInter-frequency measurement system information in SIB 11/12InformationSemanticsElement/Group nameMultiType and referencedescriptionInter-frequency cell info listInter-frequency cellinfo listInter-frequency reportingInter-frequencyquantity for RACHreporting quantity forReportingRACH ReportingMaximum number of inter-Maximum numberfrequencyof reported cellsReported cells on RACHon RACH
TABLE 1bInter-frequency reporting quantity for RACH reportingInformation Element/SemanticsGroup nameMultiType and referencedescriptionCHOICE mode>FDD>>Reporting quantityEnumerated(CPICH Ec/N0,CPICH RSCP, No report)>TDD>>Reporting quantity1 to 2list>>>Reporting quantityEnumerated(Timeslot ISCP,Primary CCPCH RSCP, Noreport)
TABLE 1cMaximum number of inter-frequency reported cells on RACHTypeSemanticsInformation Element/Group nameMultiand referencedescriptionMaximum number of reported cellsInteger(1 . . . 8)per for all reported non-usedfrequencies
A ‘Reporting quantity’ IE as shown in Table 1b indicates which reporting quantity is to be used when the inter-frequency measurement system information is transmitted over the RACH. For example, in a cell using Frequency Division Duplex (FDD), a chip-to-noise energy Ec/No of a Common Pilot Channel (CPICH) or a Receive Signal Code Power (RSCP) of the CPICH is used as a measurement result, or ‘No report’ can be used to transmit no inter-frequency measurement result. A ‘Maximum number’ IE as shown in Table 1c indicates the maximum number of cells to which the inter-frequency measurement results will be transmitted over the RACH.
In transmitting the RACH message including the inter-frequency measurement results, if the ‘Reporting quantity’ IE and the ‘Maximum number’ IE are included in SIB11/12, the UE writes and includes as much inter-frequency measurement results as the ‘Maximum number’ IE in the RACH message according to the ‘Reporting quantity’ IE.
For example, if the ‘Maximum number’ IE is set to ‘2’ and the ‘Reporting quantity’ IE indicates an Ec/No of the CPICH, the UE includes an inter-frequency cell info list for 2 non-used frequency band cells and CPICH Ec/No for the non-used frequency band cells in the RACH message according to the measurement results for the non-used frequency band cells whose frequencies are different from the currently used frequency. Table 2 below shows an information format of the inter-frequency measurement results included in the RACH message.
TABLE 2Measured results on RACHInformation Element/Type and Semantics group nameMultireferencedescriptionMeasurement result for current cellMeasurement results for 1 tomonitored cells on non-used <maxFreq>frequencies>Frequency infoFrequency >Inter-frequency cell infomeasurement results>>CHOICE mode>>>FDD>>>>Primary CPICH infoPrimary CPICH info>>>>CHOICE measurement One spare quantityvalue isneeded.>>>>>CPICH Ec/N0Integer(0 . . . 49)In dB. According toCPICH_Ec/No in [19].Fourteen spare valuesare needed.>>>>>CPICH RSCPInteger(0 . . . 91)In dBm. According toCPICH_RSCP_LEV in [19].Thirty-six spare valuesare needed.>>>TDD>>>>Cell parameters IdCell parameters Id>>>>Primary CCPCH RSCPPrimary CCPCHRSCP info
In this case, monitored cells consist of neighbouring cells.
ConditionExplanationDCCHThis IE is optionally present when DCCH is used and notneeded otherwise.
As shown in Table 2, in reporting the inter-frequency measurement results over the RACH message, the UE includes as much ‘Frequency Info’, ‘Primary CPICH info’ and ‘measurement quantity’ as the ‘Maximum number’ IE, transmitted through SIB11/12, in the RACH message, causing an excessive increase in the size of the RACH message.
In addition, the UE includes the measurement results for the non-used frequencies in the RACH message even though the channels states of the non-used frequencies are bad. As is known to those skilled in the art, in order to transmit a message over the RACH, the UE should first send a request for RACH transmission approval to a base station (or Node B) and receive response information indicating approval of the RACH transmission from the Node B. Therefore, when RACH transmission approval requests are issued by a plurality of UEs, each UE may fail to obtain RACH transmission approval within the ‘Maximum number’. Nonetheless, if each UE unnecessarily transmits the measurement results on several non-used frequencies over the RACH, signaling overhead of the RACH may increase excessively.
That is, in conventional measurement reporting, the measurement result information included in the RACH message includes many IEs, and there is no criterion for reporting, by the UE, the measurement results over the RACH, causing an increase in an uplink load.
Accordingly, a need exists for a system and method for effectively and efficiently reporting measurement results.